1. Field of the Invention
The invention relates to an illuminant module, and more particularly, an illuminant module comprising an optical film with alternatively arranged specific concave surfaces and convex surfaces to diffuse light from light emitting diodes.
2. Description of the Related Art
As light emitting diodes (LEDs) have high efficiency, they are gradually being more frequently applied to illumination products. When brightness in increased, the light intensity from a single spot is increased. High brightness LEDs have a dazzle problem, which is uncomfortable for human eyes. Because an LED has directional properties, brightness is concentrated on central portions, which is not suitable for illumination. Although the efficiency of a single LED can exceed 80 lm/W, the luminous flux of a single LED for ordinary illumination cannot exceed 500 lm, thus practically, more than one LED must be used for illumination. The combination of more than one LED may cause multiple shadows, which, if applied in a reading situation, influences reading. A conventional technique for solving the multiple shadow problem is to group a plurality of LEDs together or install a diffusion plate. However, for the grouping of a plurality of LEDs technique, a heat dissipation problem may occur and the dazzle problem may worsen. As for the diffusion plate technique, luminous flux may be reduced, and because the number of LEDs must be increased, the heat dissipation problem may worsen. In addition to the diffusion plate, a diffusion film with high haze is often used. However, the diffusion film cannot diffuse the high intensity light of LEDs.
For an illumination device, unlike a backlight module, a simple structure is often needed, such as a single-plated structure, and high efficiency. An illumination device using LEDs often has a secondary optical deign to uniform brightness. However, some optical designs combined with the LEDs, such as an optical cap, may increase manufacturing cost and complicate the manufacturing process. Additionally, other optical designs utilizing mirror or micro lenses, which may result in more precise positioning and excellent optical diffusion and alignment focus, have higher costs. Meanwhile, while a single-typed micro lens can provide a local refraction optical path and secondary reflection, it cannot uniform the light beam from a highly luminous light source.
US patent publication No. 20050264716 discloses an LED light source comprising a column lens, a micro lens array and an LED. A large mirror is directly disposed on an LED substrate. The LED array is aligned with the tip of the micro mirror array, whereby the light beam is refracted at the tip to the diffusion dots on the micro lens array. The refracted light beam is mixed with light beams from the LEDs. However, for such a structure, when the alignment is poor, light beam is not refracted to the diffusion dots, thus there is no light mixing effect. Also, the temperature of the micro mirrors and the LED is increased by the refraction between the mirror and the substrate.
US patent publication No. 20050265029 discloses stacks of LED substrates, reflective layers and optical layers. The thicknesses and gaps of the reflective layer are controlled to obtain better optical efficiency. In such a structure, optical alignment is required.
The World patent No. WO2007050274 utilizes two secondary optical elements to diffuse short distance light beams, thereby diffusing LED light spots. A micro lens is disposed above the LED to control the incident angle to generate uniform light beams. The uniform light beam is mixed by a diffusion film. However, such a structure still needs optical alignment. Additionally, the alignment of the micro lens and the mirror is complicated, and the optical diffusion is limited by the size of the mirror.
Japan patent publication No. 2005285697 discloses an illuminant module comprising an LED array and a micro mirror array. The LED array has a size deviation when compared with the micro mirror array. The center of the LED array is located in the focus area of the micro mirror. LEDs on the outer region have a position shift with the micro mirrors of the micro mirror array. The diffused light beam can be concentrated on a specific region to increase brightness. However, such a structure limits illumination range.
Japan patent publication No. 200249326A discloses a combined micro lens array and LED array. However, the structure also needs optical alignment. Also, optical diffusion is also limited.
World patent publication No. 2005041632A2 utilizes two secondary optical element for secondary optical refraction and diffusion. The structure uses a micro lens for secondary optical diffusion rather than the mirror in the previous patents.
The described patents need alignment of the micro mirror array and the LED array to diffuse the light from an LEDs and control brightness. Thus, the structures and alignment needed disclosed in the described patents are complicated.